The invention relates to fluorescent lamps which a potential is applied to the electrodes and between the two electrodes a gas discharge takes place in a closed space.
Such fluorescent lamps are known from the German Patent No. 11 99 882. According to the German Patent No. 27 25 412 and to the U.S. Pat. No. 36 09 436 as well as according to the U.S. Pat. No. 20 01 501, the British Patent No. 518 204 and the German Patent No. 28 35 574 it is further known to place in the inner space of fluorescent lamps straight or U-shaped discharge tubes and to provide them with several discharge electrodes. According to the German Patent No. 27 25 412 it is furthermore known, that the outer wall of the discharge tube is over half of its circumference and along its entire length provided with a layer of fluorescent material. The lamps according to these patents are small, they have an Edison base and the discharge takes place in the inner discharge tube and in the outer glass tube, respectively. The electrical discharge in the discharge space produces an ultraviolet radiation that is being converted in the layer of fluorescent material into visible light. The said UV-radiation produced in the inner discharge tube participates, however, merely to a small extent in the production of visible light that is radiated from the surface of the glass tube into the environment. For this reason, the light output or the lamp efficiency of such lamps is relatively low. The electrical energy necessary for the discharge in the inner discharge tube amounts to approx. 50% of the total energy input and, as a result, merely 10% of this energy participates in the total light output of this lamp. A further disadvantage of the heretofore known lamps is the difficult attainable homogeneity of the light distribution on the surface of the lamp. A still further economic disadvantage is the plurality of discharge electrodes required by this type of lamp. Moreover, the control of such a plurality of electrodes requires a complicated and expensive electrical circuitry.
To the state of the prior art belong also lamps that are known in literature as "compact lamps". From the Osram publication, Technische-Wissenschaftliche Abhandlungen der Osram-Gesellschaft, 1986, volume 12, pp. 383 to 393, it is known that these compact lamps are provided with electronic ballast and with an Edison base and are being operated with a higher frequency of discharge current. The advantages of the compact lamp in comparison with the smaller lamps described in the patents quoted above are the smaller dimensions, the improved lamp efficiency and the negligible light flicker. While they have the mentioned advantages, these compact lamps are very expensive and the lamp efficiency is still relatively low.
In regard to the fluorescent lamp described in the German Patent No. 11 99 882, an inner element, placed in the discharge space of the lamp, is an electrically conductive construction part and serves mainly as an auxiliary starter electrode. At the same time, this construction part enlarges the so-called recombination surface of the discharge space.